1. Technical Field
The present invention relates to a focusing lens for a light-emitting diode (LED) and, more particularly, to a focusing lens for an LED, which controls a radiation angle of the LED, to locally illuminate at a long distance.
2. Discussion of Related Art
Generally, the irradiation of light illuminated by an LED, that is, the radiation angle of the LED, is very great due to the characteristic of the LED. Therefore, the LED is mainly used to irradiate a broad region or to illuminate a close distance.
Since the LED has the characteristic in that the radiation angle thereof is very great, when it is used to irradiate a local region at a long distance, the etendue occurs so that the emitted light is not effectively used.
To minimize the aforementioned problem, a focusing lens to focus the light emitted by the LED shown in FIG. 1 has been developed.
As illustrated in FIG. 1, a conventional focusing lens 10 is positioned at a position where light of an LED 2 is radiated.
In the focusing lens 10, the whole of a body 11 is composed of a material, such as transparent glass. The top surface of the focusing lens 10 is formed of an aspheric lens surface 12 which is a curved surface to bulge upward.
The focusing lens 10 of the aspheric lens allows the light of the LED 2, which is radiated at 180°, to be transmitted through the flat bottom surface of the focusing lens 10 and to be concentrated on the aspheric lens surface of the top surface of the focusing lens 10, at the radiation angle which is less than about 150, to be irradiated.
The aforementioned conventional focusing lens 10 somewhat improves the efficiency of concentrating light around an optic axis 4 by the aspheric lens surface 12. However, the light-concentrating efficiency is restrictedly performed only around the optic axis 4. Around the edge of the focusing lens 10 which is distant from the optic axis 4, the light is refracted and diffused in an outside direction which is distant from the optic axis 4. Therefore, the conventional focusing lens 10 has a limit in locally illuminating at a long distance.